Crown 600, 1200, 2401, 2400, 601, 1201 operation manual Stereo Operation, Only ONE Channel Shown

6 Principles of Operation

6.2.1 Stereo Operation

For simplicity, the discussion of Stereo opera- tion will refer to one channel only. Mono opera- tion will be discussed later. For specific circuit references, see the block diagram in Figure 6.1.

The signal at the ¼-inch phone jack input passes directly to the balanced gain stage (U104-A and U104-B). The balanced gain stage causes balanced to single-ended conversion using a difference amplifier. From there, gain can be controlled with a potentiometer. The error amp (U104-C) amplifies the difference between the output signal and the input signal from the gain pot, and drives the voltage trans- lator stage.

From the error amp, the voltage translator stage routes the signal to the Last Voltage Amplifiers (LVAs) based on signal polarity. The +LVA

ONLY ONE CHANNEL SHOWN

(Q105) and the –LVA (Q110), with their push- pull effect through the bias servo Q318, drive the fully complementary output stage.

The bias servo Q318 is thermally coupled to the heat sink and sets the quiescent bias cur- rent in the output stage to lower the distortion in the crossover region of the output signal.

D301, D302, D303, and D304 remove the charge on the unused portion of the output stage based on the polarity of the output signal.

With the voltage swing provided by the LVAs, the signal then gains current amplification through the Darlington emitter-follower output stage.

The bridge-balanced circuit (U104-D) receives a signal from the output of the amplifier and compares it to the signal at the Vcc supply. The bridge-balanced circuit then develops a voltage

Micro-Tech Series Power Amplifiers

to drive the bridge-balanced output stage. This results in the Vcc supply having exactly one half of the output voltage added to their quies- cent voltage. D309, D310, D311 and a trimmer resistor set the quiescent current point for the bridge-balanced output stage.

The protection mechanisms that affect the sig- nal path are implemented to protect the ampli- fier under real-world conditions. These conditions are high instantaneous current, excessive temperature, and output device oper- ation outside safe conditions.

Q107 and Q108 sense output current and act as a common current limiter. When instantaneous current exceeds the design criteria, the limiters remove the drive from the LVAs to limit output current to safe levels.

Figure 6.1 Circuit Block Diagram

page 16 Operation Manual